1. Technical Field
The present invention relates to a method of producing metal nanoparticles and the metal nanoparticles thus produced, and in particular, to metal nanoparticles of core-shell structure and its manufacturing method.
2. Description of the Related Art
General ways to produce metal nanoparticles are the vapor-phase method, the solution (colloid) method and a method using supercritical fluids. Among these methods, the vapor-phase method using plasma or gas evaporation is generally capable of producing metal nanoparticles with the size of several tens of nm, but has limitation in synthesizing small-sized metal nanoparticles of 30 nm or less. Also, the vapor-phase method has shortcomings in terms of solvent selection and costs, particularly, in that it requires highly expensive equipments.
The solution method including thermal reduction and phase transfer is capable of adjusting various sizes of metal nanoparticles, synthesizing several nm sizes of metal nanoparticles having uniform shape and distribution. However, the production of metal nanoparticles by this existing method provides very low yield rate, as it is limited by the concentration of the metal compound solution. That is, it is possible to form metal nanoparticles of uniform size only when the concentration of the metal compound is less than or equal to 0.01M. Thus, there is a limit also on the yield of metal nanoparticles, and to obtain metal nanoparticles of uniform size in quantities of several grams, chemical reactor of 1000 liters or more is needed. This represents a limitation to efficient mass production. Moreover, the phase transfer method necessarily requires a phase transfer, which is a cause of increased production costs.
In case of forming fine wirings with these metal nanoparticles, precious metals such as gold, silver, palladium, platinum are preferable with respect to conductivity. However, since these metals are expensive and cause increase of production cost of electronic devices, the use of copper which has desired conductivity and economical efficiency is needed. However, if copper is used to produce nanoparticles, it is oxidized easily and an oxidized layer is formed on the surface so that the conductivity decreases rapidly. Therefore, in spite of increase of production cost, precious metals such as silver are used to produce a fine wiring.
Moreover, in case of forming wirings with silver, since metal nanoparticles gather together to the margin area in a wiring unit or in droplets of conductive ink which will form the wiring, the migration that metal is precipitated at a cathode according to ionization of metals, may easily occur. Therefore, there is a risk that may cause potential inferiority even after formation of wiring, actually the inferiority caused by the migration of silver incurs the inferiority of entire goods.